Molded plastic parts have becoming increasingly popular, due at least in significant part to their low production cost, good chemical resistant properties, high strength, and heat resistance. Hence, often, one or more components of an assembly are formed of molded plastic. In assembling a final product it is often necessary to fasten the molded plastic parts to other components to produce the final product. Many plastic parts are molded of acrylic, polycarbonate or other similar material due to their high strength. However, such materials also have low ductility, and it is often desirable to screw a threaded member or fastener into a molded plastic part to fasten another component thereto.
Current production methods for fastening components to a plastic part include forming a threaded recess in the plastic part, which serves as a base, and into which a threaded member or fastener is screwed. This has been found to be undesirable in several respects. The brittle nature of the plastic employed makes it difficult to cut threads in the acrylic base for receiving the threaded member. During molding of the plastic part,  strength is obtained from a hardened “skin;” however, this hardened “skin” is broken when a thread is cut into the plastic. As such, during thread formation, the plastic base material has been found to crack and chip, often making insertion of the threaded fastener difficult or impossible. Also, the chipping reduces the bearing surface area against which the threads of the fastener bear against the base to preclude the fastener from being pulled out of the base. Thus, the load bearing capacity of the threaded member is significantly reduced.
Due to the aforementioned difficulties associated with pre-threading brittle plastic base materials, other, less desirable, fastening means have been employed. One such alternative fastening means attempted has been to employ a self-threading screw. However, the brittle nature of the plastic base material precludes the formation of a consistent thread therein, with a resultant cracking of the base.
Alternatively, internally threaded metal inserts have been molded to the base, with a threaded fastener then screwed into the internal threads of the metal insert. The formation of the metal inserts adds considerable expense to the overall production cost. Additionally, because metals are generally much stronger than plastic, the use of metal inserts is overkill as the pull strength of the metal is much higher than that required for plastic devices and the base plastic generally will break before the metal insert upon application of a sufficient pulling force.
One method currently employed for fastening components to the base which provides the desired bonding strength is a conventional screw and nut assembly. However, this is undesirable in several respects. Functionally, the screw and nut assembly loosens over time, resulting in a loose connection between components. Also,  aesthetically, screw and nut assemblies are undesirable due to the requirement of a provision for accommodating the nut or the nut being exposed on one end of the base, rather than allowing for employment of a blind tapping which provides superior aesthetics. Furthermore, the requirement of the metal nut adds cost to production and is difficult to automate.
U.S. Pat. Nos. 5,222,850 and 5,391,031, both to Medal, disclose a plastic insert having a plurality of wedge shaped protrusions on the outer wall of the insert. The protrusions are melted after inserting into a plastic base to blend with the plastic immediately surrounding the insert to form a bond with the base. Because of the shape and location of the protrusions, complicated molds must be designed to accommodate the undercut between the protrusions along the length of the insert. Additionally, both the plastic and the base material must be melted to effect proper bonding to the insert and base material.
There is a need for a fastener and method of fastening components to a plastic base material which provides a good, secure connection capable of withstanding significant separating forces without added complication of bonding the insert to the base material. The fastener should also lend itself to low production cost and provide a reusable thread for disassembly and assembly without compromising joint strength. 